"SEPTEMBER 1993 will go down in net.history as the September that never ended," wrote Dave Fischer in an internet posting in January 1994. Mr Fischer, an early digital artist, was talking about the move by AOL, then the biggest internet service provider, to let its customers participate in a threaded newsgroup system called Usenet, previously the preserve of academics, government and military types. Prior to 1993 September was when each year university IT departments issued a new crop of uppity 18-year-old geeks with account logins that came with access to time-sharing systems on mainframes—and so, too, to the inchoate internet. Before long, though, the freshmen would be put in their place (or, more likely, would switch to quaffing beer).

AOL's decision meant that each day was as the first day of school—with a constant influx of "newbies", as the old guard disparagingly labelled first-time users with no knowledge of the tacit rules which had allowed newsgroups to function smoothly. The web may have aged into October, but any new service that reaches a critical mass lives through its own "eternal September", as the phenomenon came to be known.

In the era of social networks thousands of users can turn into hundreds of thousands, even millions, in a matter of weeks. This makes September especially febrile. Existing users, in particular early adopters who had braved beta tests and server failures, are prissy about the "noobs" who don't know the rules—or, worse, fiddle with them. Eventually, though, their number plateaus and services switch from reeling in new customers to keeping existing ones happy, so that they do not start pining for another autumn jaunt elsewhere.

Instagram, a photo-sharing service, has already lived through one metaphorical September (in fact, October 2010), when the service hit a million users of its iPhone and iPad app within weeks of launch. People loved how it let them degrade pictures they took to resemble those made using old snapshot cameras (something your correspondent never quite understood). Nowadays, the unspoken rule seems to dictate that every other photo on Facebook, Flickr or Twitter must be Instagrammed.

On April 3rd it released a long-awaited version of its software for Google's Android operating system, which powers at least 200m smartphones, most of them advanced enough to run Instagram. The Android app was downloaded a million times in the first 24 hours. (On April 9th the firm announced its acquisition by Facebook for $1 billion in stock and cash, a significant premium over its previous private valuation.)Predictably, a spate of articles and blog posts has already begun to sprout, with existing Instagram users fretting about the cluelessness and ineptitude of Android parvenus elbowing their way into the blurry photostream. Carps abound about Twitter feeds overwhelmed with a flood of banal photographs of yellowed grainy parking meters and solarised shots of streetlamps at night. Or Facebook friends' snapshots of people and routine occurrences suddenly all aping New Wave album covers. It may be April, but September is here again.